Thesis (M.S.)--University of Wisconsin--Madison, 1965. / eContent provider-neutral record in process. Description based on print version record. Bibliography: l. 80.

La rareté de la ressource en eau est maintenant reconnue comme une limitation critique à la progression de la production agricole des prochaines décennies. De plus, la demande de nourriture sera sujette à l'augmentation, alors qu'il est attendu que la population mondiale atteigne 8.6 milliards en 2030 et 9.8 milliards en 2050. La pomme de terre est la 4e culture la plus importante au monde derrière le blé, le maïs et le riz. Parmi ces cultures, la pomme de terre est la plus efficace en production de calorie par litre d'eau. Cependant, les rendements de pommes de terre sont reconnus comme sensibles aux manques d'eau. La pression exercée par la production agricole peut aussi compromettre la santé du sol en affectant divers indicateurs tels que la stabilité structurale du sol, la masse volumique, la conductivité hydraulique et le taux de carbone organique. Préserver la santé du sol est un enjeu critique afin de maintenir les services écosystémiques des sols comme la filtration et le stockage de l’eau, le cyclage des nutriments du sol et le stockage du carbone. L'objectif de cette thèse était de concevoir une approche d’irrigation intégrée appliquée à la production de pommes de terre qui permettrait une utilisation efficace de l'eau et l'atteinte de rendements optimaux tout en minimisant les externalités environnementales négatives de l'irrigation. Dans cette étude, les effets de la gestion de l'irrigation sur les rendements de différentes variétés de pommes de terre, sur l'efficacité d'utilisation de l'eau, sur la distribution des tubercules et sur la dynamique du carbone organique ont été analysés et temporalisé. Pour ce faire, six expériences en serre ont été menées à l'aide d’un système d’irrigation automatisé contrôlé à partir des données d’un réseau de tensiomètres. Dans les chapitres deux et trois, l’impact de seuil d'irrigation de précision a été évalué sur les rendements de quatre variétés ayant des classes de maturité différente (Envol : très hâtive, Kalmia : hâtive, Goldrush : mi-saison, et Red Maria : tardive). Une zone de confort hydrique optimale pour les plants de pommes de terre a été identifiée entre−10 et −24 kP a. Les seuils identifiés ne sont pas dépendants de la classe de maturité, de la hauteur des plants ou de la production potentielle de tubercule. Le seuil de −24 kP a est celui qui a permis d’atteindre des rendements maximaux tout en optimisant l’efficacité de l'utilisation de l’eau. Le temps passé dans la zone de confort a aussi été identifié comme critique pour le développement des rendements de la pomme de terre. L'analyse de l'effet temporel des seuils d'irrigation sur les rendements de pomme de terre effectuée dans le chapitre trois a aussi montré qu’une gestion précise de l'irrigation est nécessaire dès le stade du développement foliaire et qu'elle devrait être maintenue jusqu'à la maturité. Une gestion appropriée de l'irrigation a permis une augmentation des rendements entre 25 et 40%. L'impact de quatre seuils de potentiel matriciel (−10, −20, −30, et −45 kP a) sur la distribution spatiale des tubercules a été évalué à l'aide de la tomodensitométrie à rayonX (CT-scan) dans le chapitre quatre. Une relation linéaire entre les seuils d'irrigation et la profondeur des tubercules a été identifiée. Une gestion de l'irrigation à des seuils entre −20 et −30 kP a a permis une profondeur des tubercules optimale permettant une meilleure efficacité de récolte et limitant la prépondérance des maladies en surface. Les seuils de potentiel matriciel utilisé dans cette étude ont influencé le taux de décomposition du carbone organique du sol, évalué dans le chapitre cinq. Une décomposition plus élevée a été observée au seuil de −15 kP a. Les seuils d'irrigation se sont démarqués dans le second quart de la saison de croissance, aux stades d’initiation et de grossissement des tubercules, des stades à forte croissance et de fréquence d’irrigation accélérée. La création d’une approche de gestion de l'irrigation intégrée permettra au producteur de pommes de terre d’adapter leur gestion de l’eau à la ferme et d’intégrer des pratiques plus durables tout en atteignant des rendements plus élevés et une plus grande efficacité de l'utilisation de l'eau. L'amélioration de leur gestion de l'eau du sol pourrait aussi permettre d'optimiser la distribution spatiale des tubercules, d’augmenter l'efficacité de la récolte et de réduire la décomposition du carbone créant un système de culture qui favoriserait une meilleure conservation de la santé du sol. / Water scarcity is increasingly recognized as the most pressing limitation to improvement in agricultural production over the upcoming decades. It is expected that the world population will reach 8.6 billion by 2030 and 9.8 billion by 2050, increasing the demand for both food and agriculture production. Therefore, increasing overall water productivity is one of the most critical challenges of the twenty-first century. Potato isthe fourth most cultivated food crop behind wheat, maize, and rice. Among the major crops, potato is the most efficient in calory production by water liter, but potato yields are recognized as sensitive to water stress. Therefore, the precise control of the amount of irrigation water, water application timing, and prevailing micro-meteorological conditions are critical factors that influence the plant health and yield. However, the increasing pressure on agricultural systems can endanger soil health, as several soil health indicators are affected by agricultural production, like soil structural stability, bulk density, hydraulic conductivity, and soil organic carbon. Maintaining soil healthis critical to preserve soil ecosystemic functions like water infiltration, filtration andstorage, nutrient cycling, and carbon storage, impacting plants productivity, and wateruse efficiency. The objective of this thesis was to create an integrated irrigation approach for the potato crop, allowing optimal potato yield, water use efficiency, and minimizing the environmental impact of irrigation. Through six green house experiments using an automatic irrigation system managed using a soil sensors network, the effect of irrigation management on the potato varieties, potato yield, water use efficiency, tuber spatial distribution, and soil organic carbon dynamics has been analyzed and temporalized. The second and third chapters of this study evaluated the effect of precision irrigation thresholds on the potato yields of four varieties with different maturity classes (Envol: very early, Kalmia: early, Goldrush: mid-season, and Red Maria: mid-late). Anoptimal comfort zone between −10 and −24 kP a has been identified. The optimal irrigation thresholds identified were not dependant on maturity class, plant height, or tuber potential production. The −24 kP a is the precision irrigation threshold that allowed higher yields and water use efficiency. The time spent in the comfort zone was identified as critical for the potato yield. The analysis of the irrigation thresholds'temporal effect made in the third chapter showed that precise irrigation managementis needed early in the season and should be maintained throughout all the growingseason as the critical period identified corresponded to the leaf expansion and tuber initiation stage. An appropriate irrigation management of potato crops has been shownto increase yield by a 25 to 40% margin. The fourth chapter evaluated the impact of four soil matric potential (−10, −20, −30,and −45 kP a) on potato tubers’ spatial distribution using an X-ray CT scanner. Alinear relationship between irrigation thresholds and potato tuber depth was identified.The deepest tuber distribution was observed with the −10 kP a treatment. Potato irrigation management using a SMP threshold between −20 and −30 kP a could reduce the harvest depth. Reducing the harvest depth could decrease the negative impacts of soil disturbance on soil structural stability. In the −45 kP a treatment, the tubers were too close to the soil surface, which could lead to a greater preponderance of tuber diseases like late blight or greening. The precision irrigation threshold used in this study affected the decomposition rate of soil organic carbon, evaluated in the fifth chapter. Faster decomposition of labile organic carbon was promoted by water excess (−15 kP a). The dryer (−30, −45, and −60 kP a) precision irrigation thresholds did not show any differences. The difference between the precision irrigation thresholds was made in the second quarter of the growing season,between 38 and 53 days after planting. This critical period occurred in a stage of strong vegetative growth and rapid irrigation cycles, the tuber initiation and tuber bulking stages. The determination of an integrated irrigation management approach will allow potato growers to adapt their farm management processes to integrate more sustainable water management practices and to achieve higher yields and water use efficiency. Improving soil water management may also optimize tuber spatial distribution, enhance harvest efficiency, reduce greenhouse gas emissions, soil carbon degradation, and soil disturbance in the cropping systems to benefit global soil health conservation.

The Mississippi River Valley Alluvial Aquifer (MRVAA) is declining precipitously due to irrigation withdrawal for row-crops. The development of scientific irrigation scheduling techniques and for soybean (Glycine max L.) will reduce withdrawal from the MRVAA. The objective of this research was to determine if soybean grain yield, irrigation water use efficiency (IWUE), and net return above irrigation cost could be optimized using a static irrigation threshold or if the irrigation threshold should be changed as a function of plant growth stage.

A well-managed irrigation scheduling system needs a rapid, preCIse, simple, costeffective and non-destructive soil water content sensor. The PRl profile probe and Diviner 2000 were used to determine the timing and amount of irrigation of three cover crops (Avena sativa L., Secale cereale L. and Lolium multiflonlm Lam.), which were planted at Cedara, KwaZulu-Natal. The PRl profile probe was first calibrated in the field and also compared with the Diviner 2000. For the calibration of the PRl profile probe the factory-supplied parameters (aJ = 8.4 and ao = 1.6) showed good correlation· compared to the soil-estimated parameters (aJ = 11.04 and ao = 1.02). The factorysupplied parameters gave a linear regression coefficient (r2 ) of 0.822 and root mean square error (RMSE) of 0.062. The soil-estimated parameter showed a linear regression coefficient of 0.820 with RMSE of 0.085. The comparison between the soil water content measured using the PR1 profile probe and Diviner 2000 showed a linear regression coefficient of 0.947 to 0.964 with a range of RMSE of 0.070 to 0.109 respectively for the first 100 to 300 mm soil depths. The deeper depths (400, 600 and 1000 mm) showed a linear regression coefficient ofO.716to 0.810 with a range of 0.058 to 0.150 RMSE. These differences between the shallow and deeper depths could be due to soil variability or lack of good contact between the access tube and the surrounding soil. To undertake irrigation scheduling using the PRl profile probe and Diviner 2000, the soil water content limits were determined using field, laboratory and regression equations. The field method was done by measuring simultaneously the soil water content using the PR1 profile probe and soil water potential using a Watermark sensor and tensiometers at three depths (100, 300 and 600 mm) from a 1 m2 bare plot, while the soil dries after being completely saturated. The retentivity function was developed from these measurements and the drained upper limit was estimated to be 0.355 m3 m-3 when the drainage from the pre-wetted surface was negligible. The lower limit was calculated at -1500 kPa and it was estimated to be 0.316 m3m,3. The available soil water content, which is the difference between the upper and lower limit, was equal to 0.039 m3 m,3. In the laboratory the soil water content and matric potential were measured from the undisturbed soil samples taken from the edge of the 1 m2 bare plot before the sensors were installed. Undisturbed soil samples were taken using a core sampler from 100 to 1000 mm soil depth in three replications in 100 mm increments. These undisturbed soil samples were saturated and subjected to different matric potentials between -1 to -1500 kPa. In the laboratory, the pressure was increased after the cores attained equilibrium and weighed before being subjecting to the next matric potential. The retentivity function was then developed from these measurements. The laboratory method moved the drained upper limit to be 0.390 m3 m,3 at -33 kPa and the lower limit be 0.312 m3m-3 at -1500 kPa. The regression equation, which uses the bulk density, clay and silt percentage to calculate the soil water content at a given soil water potential, estimated the drained upper limit to be 0.295 m3m-3at -33 kPa and the lower limit 0.210 m3 m,3 at -1500 kPa. Comparison was made between the three methods using the soil water content measured at the same soil water potential. The fieldmeasured soil water content was not statistically the same with the laboratory and estimated soil water content. This was shown from the paired-t test, where the probability level (P) for the laboratory and estimated methods were 0.011 and 0.0005 respectively at 95 % level of significance. However, it showed a linear regression coefficient of 0.975 with RMSE of 0.064 when the field method was compared with the laboratory method. The field method showed a linear regression coefficient of 0.995 with RMSE of 0.035 when compared with the estimated method. The timing and amount of irrigation was determined using the PR1 profile probe and Diviner 2000. The laboratory measured retentivity function was used to define the fill (0.39 m3 m-3 ) and high refill point (0.34 m3 m-3 ). The soil water content was measured using both sensors two to three times per week starting from May 29 (149 day of year, 2002) 50 days after planting until September 20 (263 day of year) 11 days before harvesting. There were five irrigations and twenty rainfall events. The next date of irrigation was predicted graphically using, the PRl profile probe measurements, to be on 3 September (246 day of year) after the last rainfall event on 29 August (241 day of year) with 8 mm. When the Diviner 2000 was used, it predicted two days after the PRl profile probe predicted date. This difference appeared since the Diviner 2000-measured soil water content at the rooting depth was slightly higher than the PRl profile probe measurements. The amount of irrigation was estimated using two comparable methods (graphic and mathematical method). The amount of irrigation that should have been applied on 20, September (263 day of year) to bring the soil water content to field capacity was estimated to be 4.5 hand 23 mm graphically and 5.23 hand 20 mm mathematically. The difference between these two methods was caused due to the error encountered while plotting the correct line to represent the average variation in soil water content and cumulative irrigation as a function of time. More research is needed to find the cause for the very low soil water content measurements of the PRI profile probe at some depths. The research should be focused on the factors, which could affect the measurement of the PRl profile probe and Diviner 2000 like salinity, temperature, bulk density and electrical conductivity. Further research is also needed to extend the non-linear relationship between the electrical resistance of the sensor and soil water potential up to -200 kPa. This non-linear equation of the Watermark is only applicable within the range of soil water potential between -10 and -100 kPa. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2003.

Limited water supplies are available to satisfy the increasing demands of crop production. It is therefore very important to conserve the water, which comes as rainfall, and water, which is used in irrigation. A proper irrigation water management system requires accurate, simple, automated, non-destructive method to schedule irrigations. Utilization of infrared thermometry to assess plant water stress provides a rapid, nondestructive, reliable estimate of plant water status which would be amenable to larger scale applications and would over-reach some of the sampling problems associated with point measurements. Several indices have been developed to time irrigation. The most useful is the crop water stress index (CWSI), which normalizes canopy to aIr temperature differential measurements, to atmospheric water vapour pressure deficit. A field experiment was conducted at Cedara, KwaZulu-Natal, South Africa, to determine the non-water-stressed baselines, and CWSI of cereal rye (Secale cereale L.) from 22 July to 26 September 2002, and aImual (Italian) ryegrass (Lolium multiflorum Lam.) from October 8 to December 4, 2002, when the crops completely covered the soil. An accurate measurement of canopy to air temperature differential is crucial for the determination of CWSI using the empirical (Idso et al., 1981) and theoretical (Jackson et al., 1981) methods. Calibrations of infrared thermometers, a Vaisala CS500 air temperature and relative humidity sensor and thermocouples were performed, and the reliability of the measured weather data were analysed. The Everest and Apogee infrared thermometers require correction for temperatures less than 15 QC and greater than 35 QC. Although the calibration relationships were highly linearly significant the slopes and intercepts should be corrected for greater accuracy. Since the slopes of the thermocouples and Vaisala CS500 air temperature sensor were statistically different from 1, multipliers were used to correct the readings. The relative humidity sensor needs to be calibrated for RH values less than 25 % and greater than 75 %. The integrity of weather data showed that solar irradiance, net irradiance, wind speed and vapour pressure deficit were measured accurately. Calculated soil heat flux was underestimated and the calculated surface temperature was underestimated for most of the experimental period compared to measured canopy temperature. The CWSI was determined using the empirical and theoretical methods. An investigation was made to determine if the CWSI could be used to schedule irrigation in cereal rye and annual rye grass to prevent water stress. Both the empirical and theoretical methods require an estimate or measurement of the canopy to air temperature differential, the non-waterstressed baseline, and the non-transpiring canopy to air temperature differential. The upper (stressed) and lower (non- stressed) baselines were calculated to quantify and monitor crop water stress for cereal rye and annual ryegrass. The non-water-stressed baselines were described by the linear equations Te - Ta = 2.0404 - 2.0424 * VPD for cereal rye and Te - Ta = 2.7377 - 1.2524 * VP D for annual ryegrass. The theoretical CWSI was greater than the empirical CWSI for most of the experimental days for both cereal rye and annual ryegrass. Variability of empirical (CWSI)E and theoretical (CWSI)T values followed soil water content as would be expected. The CWSI values responded predictably to rainfall and irrigation. CWSI values of 0.24 for cereal rye and 0.29 for annual ryegrass were found from this study, which can be used for timing irrigations to alleviate water stress and avoid excess irrigation water. The non-water-stressed baseline can also be used alone if the aim of the irrigator is to obtain maximum yields. However the non-water-stressed baseline determined using the empirical method cannot be applied to another location and is only valid for clear sky conditions. And the non-water-stressed baseline determined using theoretical method requires computation of aerodynamic resistance and canopy resistances, as the knowledge of canopy resistance, however the values it can assume throughout the day is still scarce. The baseline was then determined using a new method by Alves and Pereira (2000), which overcomes these problems. This method evaluated the infrared surface temperature as a wet bulb temperature for cereal rye and annual ryegrass. From this study, it is concluded that the infrared surface temperature of fully irrigated cereal rye and annual ryegrass can be regarded as a surface wet bulb temperature. The value of infrared surface temperature can be computed from measured or estimated values of net irradiance, aerodynamic resistance and air temperature. The non-water-stressed baseline is a useful concept that can effectively guide the irrigator to obtain maximum yields and to schedule irrigation. Surface temperature can be used to monitor the crop water status at any time of the day even on cloudy days, which may greatly ease the task of the irrigator. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2003

Thesis (Ph.D.). / Written for the Dept. of Bioresource Engineering. Title from title page of PDF (viewed 2008/02/12). Includes bibliographical references.

Thesis (Ph. D.)--Cornell University, August, 1987. / Typescript. Vita. Includes bibliographical references (leaves 270-281). Also issued in print.

Thesis (Ph. D.)--Cornell University, August, 1987. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 270-281).

Thesis (Ph. D.)--Kansas State University, 2005. / Includes bibliographical references (leaves 97-100).

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